1. Field of the Invention
The present invention relates to a form rolling apparatus for manufacturing screws, gears, shafts, pipes and the like by rolling operations, and more specifically to a round die type form rolling apparatus which clamps a work between a pair of round dies and rolls the work in circumferential and axial directions by rotating the round dies.
2. Description of the Related Art
A conventionally known round die type form rolling apparatus of this kind is shown in FIG. 1 and FIG. 2. The round die type form rolling apparatus 1 rotates a pair of round dies 2a, 2b and pushes the rotating round dies symmetrically toward the center of a work 4 by hydraulic mechanisms 3a, 3b to apply a rolling pressure in the radial direction of the work 4 and thereby roll the work 4. On a base 5 are installed a pair of slide rails 6a, 6b, on which are laterally slidably mounted a pair of die moving blocks 7a, 7b that rotatably support a pair of round dies 2a, 2b. Fixedly mounted on the base 5 are a pair of pressure plates 8a, 8b to which the hydraulic mechanisms 3a, 3b are secured. Front ends of cylinder shafts 9a, 9b of the hydraulic mechanisms 3a, 3b are secured to the pair of the die moving blocks 7a, 7b, respectively. Between the round dies 2a, 2b is disposed a work support stand 10 that supports the work 4. During the rolling operation, the hydraulic mechanisms 3a, 3b are operated to drive a pair of the die moving blocks 7a, 7b toward each other, while rotating the round dies 2a, 2b, to form gears and screws.
In the conventional round die type form rolling apparatus 1 described above, however, when the hydraulic mechanisms 3a, 3b apply rolling pressures to the work 4, reaction forces P are produced between a pair of the round dies 2a, 2b as shown in FIG. 2. The reaction forces P are transmitted to the pressure plates 8a, 8b, causing the pressure plates 8a, 8b cantilevered on the base 5 to deflect and open upwardly as shown by two-dotted chain lines in the figure. When the pressure plates 8a, 8b are open, the cylinder shafts 9a, 9b are tilted, causing the die moving blocks 7a, 7b to pivot about their lower portions supported on the slide rails 6a, 6b and open upwardly as do the pressure plates 8a, 8b. Hence, the round dies 2a, 2b escape outwardly upwardly from the work 4. Therefore, the die moving blocks 7a, 7b, even when positioned correctly, move away from the work, making it impossible to form threads in the work 4 with high precision or, in the case of a gear, producing errors in a tooth shape of the work.
There is another drawback with the conventional round die type form rolling apparatus. When performing a so-called continuous rolling whereby an elongate work A longer than the widths of the round dies 2a, 2b is rolled, the conventional rolling process involves manually tilting main shafts 11a, 11b of the round dies 2a, 2b, fixing their tilt angles, with lead angles at contact portions between the round dies 2a, 2b and the work 4 kept aligned with each other, and moving the work 4 in the axial direction. With this method the tilt or inclination angle cannot be changed during the rolling operation, rendering versatile rolling operations on a work impossible.
When forming threads in the work 4, as the round dies 2a, 2b are progressively pressed against the work 4, the diameter of the root of a thread decreases. As a result, the circumferential length of the work. 4 at the root of the thread is shorter at the completion of threading or inscription than at the start of the threading. FIG. 3 shows the relation between the circumferential length of the work 4 and the pitch. The circumferential length of the work 4 decreases by xcex4L from the circumferential length L at the start of the threading to the circumferential length L1 at the completion of the threading. With the conventional round die type form rolling apparatus 1, however, because the main shafts 11a, 11b cannot be inclined vertically during rolling operation, the lead angle xcex2 is kept constant even when the thread""s root diameter of the work 4 changes. As a result, a deviation in pitch xcex4P occurs between a pitch P of the work 4 at the start of the threading and a pitch P1 at the completion of the threading, with the result that the work 4 moves axially by a distance of the pitch deviation xcex4P during the rolling operation. The phenomenon that the work 4 moves in the axial direction during the rolling operation is called a stepping or walking of the work 4 and this becomes most conspicuous when threads to be formed have a large difference between an external diameter and a root diameter. When the walking occurs, a flank of a screw thread on the same side as the direction of the walking-induced movement of the work 4 contacts the round dies 2a, 2b with an increased force, whereas a flank on the side opposite the direction of the walking-induced movement of the work 4 contacts the round dies 2a, 2b with a reduced force, giving rise to a problem of degraded finish precision of the rolled surfaces.
Further, when the work 4 is to be formed with serrations as shown in FIG. 4, the process involves bringing the main shafts 11a and 11b close to each other to slowly push the round dies 2a, 2b from positions indicated by two-dotted chain line in the figure toward the work 4. As a result, a root circle that connects roots 4a of the work 4 becomes small from a size indicated by two-dotted chain line in the figure to a size indicated by solid line. Because the modules of the round dies 2a, 2b are constant, as the root circle decreases in size, a large deviation occurs locally between a pitch formed in the work 4 at the start of inscription and a pitch formed in the work 4 at the completion of inscription. In the conventional round die type form rolling apparatus 1, because a pair of round dies 2a, 2b are rotated at the same speed by a combination of gears, this local pitch deviation cannot be absorbed, with the result that some tooth surfaces of the work 4 contact the dies with an increased force and other tooth surfaces with a reduced force. This in turn deteriorates the finish precision of the rolled tooth surfaces.
The conventional apparatus has still another problem. When the rolling operation is started, the round dies 2a, 2b are applied at the work contact surfaces with a force Fp, or a die load, in a direction normal to the dies and a force Ft in a tangential direction Ft. In the conventional round die type form rolling apparatus 1, because the main shafts 11a, 11b are controlled to rotate at a constant speed and move under a constant pressure or at a constant speed, both of the die load Fp and a rolling torque T acting on the main shafts 11a, 11b of the round dies 2a, 2b change between the start and completion of the rolling operation. The main shaft torque T, in particular, exhibits a temporary sharp increase or peak during the rolling operation. Because the peak of the main shaft torque T has a grave effect on the life of the round dies 2a, 2b, any increase in the peak value will lead to a reduced die longevity.
A first object of the present invention is to prevent the round dies from escaping outwardly upwardly due to the reaction force from the work when the work is applied with a rolling pressure.
A second object of the invention is to diversify the rolling operation on the work and to improve the finish precision of rolled surfaces by suppressing the walking of the work during the rolling operation.
A third object of the intention is to improve the finish precision of tooth surfaces when the work is formed with axial grooves such as serrations and splines.
A fourth object of the invention is to prevent a temporary increase in the machining torques acting on the main shafts of the round dies during the rolling operation to extend the longevity of the dies and improve the efficiency of the rolling operation.
To achieve the above objectives, a round die type form rolling apparatus according to the invention comprises: a set of die moving blocks rotatably supporting a set of round dies; two or more beam shafts disposed around a rolling position of a work being rolled by the round dies and extending between the set of die moving blocks; and a push mechanism for moving the set of die moving blocks toward each other; wherein the die moving blocks are moved, guided by the beam shafts, toward each other and reaction forces generated between the set of round dies by a rolling pressure are borne by the beam shafts.
A round die type form rolling apparatus according to another aspect of the invention comprises: a base; a first die moving block mounted on one end portion of the base; a pressure plate mounted on the other end portion of the base; two or more beam shafts disposed around a rolling position of a work and having both ends thereof mounted to the first die moving block and the pressure plate; a second die moving block disposed between the first die moving block and the pressure plate and guided by the beam shafts; a die push mechanism disposed between the second die moving block and the pressure plate; and a first round die and a second round die rotatably supported on the first die moving block and the second die moving block, respectively; wherein at least one of the first die moving block, the pressure plate and the second die moving block is rigidly fixed on the base, with the others slidably disposed, and the die push mechanism is operated to move the first die moving block and the second die moving block toward each other to roll the work between the first round die and the second round die.
A round die type form rolling apparatus according to still another aspect of the invention comprises: a base; a first die moving block mounted on one end portion of the base so that it is slidable to left and right; a pressure plate mounted on the other end portion of the base so that it is slidable to left and right; two or more beam shafts disposed around a rolling position of a work and having both ends thereof secured to the first die moving block and the pressure plate; a second die moving block disposed between the first die moving block and the pressure plate and guided by the beam shafts to slide on the base to left and right; a die push mechanism disposed between the second die moving block and the pressure plate; and a first round die and a second round die rotatably supported on the first die moving block and the second die moving block, respectively; wherein the die push mechanism is operated to slide the second die moving block guided by the beam shafts toward the rolling position, the pressure plate is slid the same distance in the opposite direction to cause the first die moving block through the beam shafts to slide the same distance toward the rolling position to roll the work between the first round die and the second round die that are disposed close to each other.
A round die type form rolling apparatus according to still another aspect of the invention is characterized in that three or four of the beam shafts are arranged in good balance around the rolling position of the work.
A round die type form rolling apparatus according to a further aspect of the invention is characterized in that a pinion is mounted on the base and that one of a pair of racks meshing with the pinion is secured to either the first die moving block or the pressure plate and the other of the pair of racks is secured to the second die moving block.
A round die type form rolling apparatus according to a further aspect of the invention is characterized by: distance detection means mounted between the set of the die moving blocks to measure a distance between the die moving blocks; and numerical control means to drive the die push mechanism based on a measured value of the distance detection means.
In a round die type form rolling apparatus which moves main shafts of rotating round dies toward a work to roll the work; the apparatus according to a further aspect of the invention is characterized by: main shaft inclination mechanisms for inclining the main shafts of the round dies in a plane perpendicular to a direction of movement of the main shafts; and a drive source for driving the main shaft inclination mechanisms.
A round die type form rolling apparatus according to a further aspect of the invention is characterized by: inclination angle detection means for detecting inclination angles of the main shafts; and control means for feeding back the inclination angles of the main shafts to control the inclination of the main shafts.
A round die type form rolling apparatus according to a further aspect of the invention is characterized in that the main shafts are inclined according to a change in a diameter of the work during the rolling operation and that a lead angle is corrected according to the change in the work diameter during the rolling operation to control the movement of the work.
A round die type form rolling apparatus according to a further aspect of the invention is characterized in that walking detection means is provided for detecting a walking of the work that occurs during the rolling of the work and that, based on a detection signal obtained by the walking detection means, the inclination angles of the main shafts are controlled to suppress the walking of the work or to hold the walking of the work constant.
In a round die type form rolling apparatus which clamps a work between a set of round dies and moves main shafts of the rotating round dies toward each other to roll the work; the round die type form rolling apparatus according to a further aspect of the invention is characterized by: servo motors for rotating the set of round dies and rotation angle detection means for detecting rotation angles of the set of round dies; and in that phases of the rotation angles of the set of round dies are changed relative to each other according to a change in a diameter of the work being rolled.
A round die type form rolling apparatus according to a further aspect of the invention is characterized in that the rotation angle detection means are directly connected to the main shafts of the round dies.
In a round die type form rolling apparatus which clamps a work between a set of round dies to roll the work; the round die type form rolling apparatus according to a further aspect of the invention is characterized by torque detection means for detecting rolling torques acting on the round dies and in that at least either revolution speeds of the round dies or moving speeds of the round dies are controlled to keep the rolling torques acting on the round dies during the rolling operation in a predetermined range.
A round die type form rolling apparatus according to a further aspect of the invention is characterized in that torque values detected by the torque detection means are compared with a set torque value and that a control is performed in such a way that when the detected torque values are higher than the set torque value, revolution speeds of the round dies are raised and that when the detected torque values are lower than the set torque value, the revolution speeds of the round dies are lowered.
A round die type form rolling apparatus according to a further aspect of the invention is characterized in that torque values detected by the torque detection means are compared with a set torque value and that a control is performed in such a way that when the detected torque values are higher than the set torque value, moving speeds of the round dies are lowered and that when the detected torque values are lower than the set torque value, the moving speeds of the round dies are raised.
With the construction described above, because the beam shafts are disposed around the rolling position of the work to be rolled by the round dies and extend between the left and right die moving blocks so as to bear the reaction forces generated between a set of the round dies by the rolling pressure, it is possible to prevent the die moving blocks from opening due to the reaction forces and the round dies from escaping outwardly upwardly as they would in the conventional apparatus. This in turn can improve the machining precision of the work.
Further, because at least one of the paired die moving blocks and the pressure plate is rigidly fixed on the base with the others slidably disposed, because the beam shafts are extended between one of the die moving blocks and the pressure plate, with the ends of the beam shafts secured to the die moving block and the pressure plate, and because the die moving blocks are moved toward each other by a single push mechanism, a simple construction using a single push mechanism can have the beam shafts bear the reactions generated between a set of the round dies.
Further, in the round die type form rolling apparatus according to the invention, a pair of the die moving blocks that are slidable to left and right and the pressure plate are mounted on the base; the beam shafts are extended between one of the die moving blocks and the pressure plate, with the ends of the beam shafts secured to the die moving block and the pressure plate; and a single push. mechanism is used to push one of the die moving block to cause both of the die moving blocks to slide simultaneously. In this construction, because the left and right die moving blocks and the pressure plate are not secured to the base, the reaction forces generated between the round dies can be shared more uniformly among the beam shafts.
Further, in the round die type form rolling apparatus according to the invention, because three or four of the beam shafts extending between a pair of the die moving blocks are disposed around the rolling position of the work in good balance, the reaction forces generated in the round dies by the rolling pressure can be shared equally among the three or four beam shafts.
Further, in the round die type form rolling apparatus according to the invention, because the pinion is mounted on the base and one of the paired racks meshing with the pinion is secured to either the first die moving block or the pressure plate and the other to the second die moving block, the center line of the work being rolled can be held stationary at all times, thus improving the machining precision of the work and facilitating the automation of supply and discharge of the work.
Further, because the round die type form rolling apparatus according to the invention includes the distance detection means mounted between a pair of the die moving blocks and the numerical control means for driving the push mechanism based on the measurement from the distance detection means, the depth of inscription formed by the round dies can be controlled with high precision.
Further, because the round die type form rolling apparatus according to the invention includes the main shaft inclination mechanisms for inclining the main shafts of the round dies in a plane perpendicular to the direction of movement of the main shafts and the drive source for the main shaft inclination mechanism, it is possible to suppress the walking of the work during the rolling operation and thereby improve the finish precision of the work and at the same time to diversify the mode of rolling by controlling the walking of the work.
Further, because the round die type form rolling apparatus according to the invention includes the inclination angle detection device for detecting the inclination angles of the main shafts and the control means for controlling the inclination of the main shafts by feeding back the inclination angles of the main shafts, the inclination angle of the main shafts can be controlled highly precisely, which in turn improves the rolling precision.
Further, in the round die type form rolling apparatus according to this invention, because the main shafts are inclined according to a change in the diameter of the work being rolled to correct the lead angle according to the change of the work diameter, the walking of the work caused by the work diameter change during the rolling operation can be prevented.
Further, in the round die type form rolling apparatus according to the invention, because the walking detection means for detecting the walking of the work is provided and because the main shafts are inclined according to a detected signal from the walking detection means to control the motion of the work, the walking of the work can be reliably prevented or held constant and the pitch kept constant, thereby improving the finish precision of the rolled surfaces.
Further, in the round die type form rolling apparatus according to the invention, the control is performed to change the rotation angles of a set of the round dies relative to each other as the diameter of the work being rolled changes, so that when the work is to be formed with axial grooves, a change in the circumferential length of the work can be distributed and absorbed among each of the pitches from the start of inscription toward the end of inscription, thereby producing smooth tooth surfaces of the work.
Further, in the round die type form rolling apparatus according to the invention, because the rotation angle detection means are directly connected to the main shafts of the round dies, the rotation angles of the round dies can be known precisely even when errors occur due to backlash and distortion in the die rotation transmission system.
Further, in the round die type form rolling apparatus according to the invention, because the machining torques acting on the round dies during the rolling operation are detected and at least one of the revolution speed and the moving speed of the round dies is controlled to bring the detected torques close to the preset torque value, it is possible to prevent the die torques from becoming large temporarily as observed in the conventional apparatus, thus extending the service life of the rolling dies and enhancing the efficiency of the rolling. Also by controlling the machining torques acting on the round dies, the depth of inscription in the work can be controlled with high precision, further improving the rolling precision.
Further, in the round die type form rolling apparatus according to the invention, the torque values detected by the torque detection means are compared with the set torque value, and when the detected torque values are higher than the set torque value, the revolution speeds of the round dies are raised and when the detected torque values are lower than the set torque value, the revolution speeds are lowered to control the detected torques to come close to the preset torque value. This makes it possible to keep the torque constant from the start of the rolling to the end and also keep the rolling time constant, which in turn makes the apparatus suitable for mass production of works.
Furthermore, in the round die type form rolling apparatus according to the invention, the torque values detected by the torque detection means are compared with the set torque value, and when the detected torque values are higher than the set torque value, the moving speeds of the round dies are lowered and when the detected torque values are lower than the set torque value, the moving speeds are raised to control the detected torques to come close to the preset torque value. This makes it possible to keep the torque constant from the start of the rolling to the end and also to know an ideal rolling time for each work.
These features and advantages of the present invention will be described in more detail by referring to the accompanying drawings